This invention relates to devices for reading and recording magnetic data, and more particularly to means for mounting the carriage/actuators assemblies provided in such devices for controlling the position of transducing heads with respect to rotatable data storage discs.
In one well known type of disc drive, magnetic data is stored on a plurality of horizontally disposed discs, spaced apart from one another and concentrically on a hub rotatable about a vertical axis. One of the recording surfaces of the disc is devoted to servo or positioning data, with the remaining recording surfaces devoted to working data. A carriage supports a plurality of transducing heads, and is movable for selective positioning of the heads generally radially of the discs. The combined carriage movement and disc rotation enable the selective positioning of each of the heads at any desired location over its associated recording surface. The carriage may be either linear or rotary. In either event, a voice coil motor is provided to control carriage movement and position.
Typically, the actuator is a rigid member attached directly to a disc drive deck or housing. The carriage/actuator and housing are subject to vibrations caused by carriage movement spindle rotation, air turbulance and the like, which is high speed and involves frequent reversals in direction. Vibration due to carriage movement causes problems within the drive, particularly at resonant frequencies. For example, a particular frequency (e.g. about 500 hertz) can create resonance and lead to data errors or settle-in delays, when switching from a track seeking mode to a track following mode. At a higher frequency of about 2 killohertz, resonance can lead to data errors due to mechanical misalignment of the working data heads with respect to the servo data head. As manufacturers cf disc drives continually seek to improve such drives by reducing access time of the heads to selected data tracks on the discs, the need to overcome the effects of unwanted vibration becomes all the more critical.
A well known expedient for reducing the energy of vibration transmitted through disc drives is the use of resilient materials to absorb vibrational energy. For example, U.S. Pat. No. 4,216,505 (Grant) discloses a means for damping transducing head vibration in tape drives. In particular, a viscoelastic polymeric layer is mounted between a transducing head shield and a metallic mass, pressing the metallic mass into frictional engagement with the transducing head. Relative displacement between the mass and transducing head is said to dampen vibrations.
U.S. Pat. No. 4,703,470 (Castaga) discloses dynamic absorbing devices for dissipating undesirable vibrations and resonances in a disc drive. A viscoelastic link element is disposed between an absorber base and an absorber mass to counter energy of vibration. The absorber base is mounted directly to the disc drive, for example on the carriage or on the base or housing below the voice coil. In an application not specifically relating to disc drives, U.S. Pat. No. 4,657,361 (Eitel et al) discloses the mounting of viscoelastic damping material between a mirror and a relatively massive mounting plate that supports the mirror, between a collar extended rearwardly of the mirror and a mounting ring that surrounds the collar, and between a rear surface of the collar and a backing plate. The bolts mounting the mounting plate to the mirror are provided with belleville or spring washers to fix the compressive load on the viscoelastic layer between the plate and mirror.
In connection with disc drives, it has been found that providing a layer of a damping tape or viscoelastic polymer between the actuator and housing substantially eliminates problems due to vibration, at least in the short run. Over time, however, the compressible viscoelastic material undergoes a creeping-type or settling deformation, due to bolt torquing or the weight of the relatively massive actuator. Another undesirable result of this deformation is that screws fastening the actuator to the housing, initially tightened to a desired torque, become relatively loose, leading to tilting and ultimately stacking height error in the multiple transducing head arrangement. The low frequency resonance problem noted above becomes more pronounced at this point. The use of belleville washers in connection with the fastening screws has been found beneficial to the extent of maintaining a consistent force upon the elastomeric layer. In spite of the improvement, undesirable creep or deformation occur when using the belleville washers. An uneven deformation of the elastomer can lead to a slight tilting of the actuator and carriage, again resulting in track following errors.
Therefore, it is an object of the present invention to provide a means for mounting a carriage and actuator assembly with respect to the rigid housing of a disc drive, to afford substantial vibration absorption and dissipation without sacrificing the positional integrity of the actuator and carriage.
Another object of the invention is to mount a disc drive actuator to a disc drive housing through a resilient layer in a manner to avoid long term deformation of the resilient layer.
Yet another object is to provide a means for mounting an actuator upon a disc drive housing to substantially prevent vertical displacement of the actuator relative to the housing, yet provide for limited horizontal displacement to generate shear stress and resultant deformation in an elastomeric layer between the actuator and housing.